Curable compositions based on polyisocyanates for coating and/or molding are well-known in the art. They provide a number of desirable characteristics such as resistance to solvent, salt, and other types of environmental attack.
However, these compositions suffer some disadvantages. Polyisocyanates can be highly difficult to handle. The NCO groups on the polyisocyanate are highly reactive, so they must be chemically blocked if it is desired to use the polyisocyanate in a one-pack curable composition. The use of chemical blocking groups further increases the expense of the material, results in increased VOC during cure, introduces an additional component into the composition that can have the potential for adverse side-effects such as yellowing, and necessitates a high heat curing temperature on the order of 150.degree. C. If the NCO groups are not chemically blocked, the polyisocyanate must be utilized as one part of a two-pack curable composition. With such a composition, the highly-reactive polyisocyanate must be kept isolated from the surrounding environment and from the other component(s) of the composition until just before application to a substrate or mold, further increasing the expense and complexity of the process.
It has thus long been desired to produce a composition that exhibits the advantages of polyisocyanate-based curable compositions having an optimum mix of characteristics as described above, but without having to use NCO groups as the functional groups for the curing reaction.